The present invention relates to a rubber composition for a base tread and a pneumatic tire using the same, particularly a rubber composition for a base tread, which has excellent fuel efficiency and steering stability, and a pneumatic tire using the same.
In recent years, demands regarding fuel efficiency are severe and low heat generation is desired in tread rubber, which occupies a high proportion of a tire. Therefore, the method of preparing a tread having a two layer structure of cap/base and using rubber having low heat generating properties for the base tread is common.
In order to reduce heat generation of the base tread, either the amount of carbon black is reduced or carbon black having large particle size is used. Also, the method of achieving both low heat generating properties and reinforcing properties by using silica and carbon black together is suggested (for example, see JP-A-2003-12866). However, in these methods, the hardness of the rubber decreases, thereby lowering the stiffness of the tire tread, and as a result, there is the problem that steering stability decreases.
Also, the method of improving air permeability resistance by compounding a laminated natural mineral in the inner liner rubber is known (for example, see JP-A-2002-88208). However, it is not described whether low heat generating properties and steering stability can sufficiently be obtained by compounding a laminated natural mineral in the base tread rubber.